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Invoke members for dispatch interfaces on that interface's corresponding IDispatch pointer, not on the canonical one - #122200
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…ing IDispatch pointer, not on the canonical one
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Pull request overview
This PR fixes a bug where dispatch interface members were being invoked on the canonical IDispatch pointer instead of the interface-specific IDispatch pointer. This caused issues when a .NET object with a custom default interface (via ComDefaultInterfaceAttribute) exposed multiple IDispatch interfaces - only the default interface's members were resolvable.
Key changes:
- Modified COM interop dispatch invocation to use the interface-specific IDispatch pointer while still validating IDispatch support via QueryInterface
- Added test infrastructure for in-process COM activation
- Added test case demonstrating the fix for non-default IDispatch interfaces
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/coreclr/vm/interoputil.cpp | Core fix: extracts and uses interface-specific IDispatch pointer for method invocation instead of canonical pointer |
| src/tests/Interop/common/ComActivationHelpers.cs | New test helper providing COM class registration and activation infrastructure |
| src/tests/Interop/COM/NETClients/ConsumeNETServer/Program.cs | Added test case validating IDispatch invocation on non-default interface, reorganized using directives, renamed TestEntryPoint to ConsumeNETServerTests |
| src/tests/Interop/COM/NETClients/ConsumeNETServer/ConsumeNETServer.csproj | Added reference to ComActivationHelpers.cs |
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AaronRobinsonMSFT
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Thank you! We should also backport this to .NET 10. I don't think it needs to go further back.
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jkoritzinsky
commented
Dec 5, 2025
@AaronRobinsonMSFT any more feedback or is this good to go? |
jkoritzinsky
commented
Dec 5, 2025
/backport to release/10.0 |
Started backporting to |
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…ce's corresponding IDispatch pointer, not on the canonical one (#122229) Backport of #122200 to release/10.0 /cc @jkoritzinsky ## Customer Impact - [X] Customer reported - [ ] Found internally [Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.] Method call on an IDispatch-based ComImport interface fails to call the target COM method if the target COM object is a .NET object exposed to COM that uses the ClassDefaultInterfaceAttribute; instead, an exception is thrown. ## Regression - [X] Yes - [ ] No [If yes, specify when the regression was introduced. Provide the PR or commit if known.] Introduced in .NET 9 #104406 ## Testing [How was the fix verified? How was the issue missed previously? What tests were added?] Added a unit test to validate the scenario and validated that the repro no longer fails. ## Risk [High/Medium/Low. Justify the indication by mentioning how risks were measured and addressed.] Low. Reverts the incorrectly functioning part of the regressing PR to the .NET 8 code path. **IMPORTANT**: If this backport is for a servicing release, please verify that: - For .NET 8 and .NET 9: The PR target branch is `release/X.0-staging`, not `release/X.0`. - For .NET 10+: The PR target branch is `release/X.0` (no `-staging` suffix). ## Package authoring no longer needed in .NET 9 **IMPORTANT**: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version. Keep in mind that we still need package authoring in .NET 8 and older versions. --------- Co-authored-by: Jeremy Koritzinsky <jekoritz@microsoft.com>
We need to invoke the method on the exact IDispatch pointer that's returned to ensure that members on that dispatch interface will be resolved. The default IDispatch pointer will only resolve members for its corresponding interface.
Fixes#122175
Regression introduced in #104406
Test helper code adapted from #122195 (can be consolidated in the future).